Recently, many kinds of liquid crystal display device mode and compensation film have been proposed to increase the viewing angle of a liquid crystal display device. An In-Plane Switching (IPS) liquid crystal display device is one typical example with a wide viewing angle. In an ISP liquid crystal display device, liquid crystal molecules move over a planar surface substantially parallel to a substrate by an electric field parallel to the substrate.
Compared to a Twisted Nematic crystal display device, an ISP liquid crystal display device provides higher contrast and better viewing angle quality for black and white displaying. However, the contrast ratio decreases at a large viewing angle due to light leaking in the dark, thereby resulting in the problems of insufficient viewing angle or color shift.
The leaking light of an off axis angle as a liquid crystal display device is in the dark state has two main reasons: (1) at an off axis viewing angle the polarizers are never orthogonal; (2) at an off axis viewing angle the optical phase retardation of liquid crystal layer changes the polarization of the incident light.
There are currently two main solutions: (1) using the phase retardation resulting from a negative optical anisotropic compensation film to compensate the phase retardation resulting from a positive optical anisotropic liquid crystal layer as disclosed in Japan Laid-Open No.2002-55341A; (2) using a wide viewing angle polarizer (see SID00 at p.1094 and Japan Laid-Open No. 2001-350022A.). However, the solution (1) does not totally solve the leaking light of an off axis angle in the dark state, wherein the leaking light results from polarizers being not orthogonal. As for the solution (2), at an off axis viewing angle, although the polarizers keep orthogonal, the leaking light of an off axis viewing angle is still caused by the optical phase retardation made from a liquid crystal layer. Therefore, these two solutions do not totally solve the leaking light in the dark state at an off axis viewing angle, and they also do not solve the general color shift as a liquid crystal display device is at an off axis sloping viewing angle in the dark state.